1. Field of the Invention
The present invention relates to a monolithic solid state power controller (SSPC) for use in the switching and distribution of power, and more specifically, for use in providing full-cycle control of power being delivered to an electrical load.
2. Description of the Prior Art
Many diverse types of power control systems have been used in the prior art for controlling the power provided to a load. Such prior art systems have included motor-driven potentiometers, magnetic amplifiers, and other diverse electrical and electro-mechanical elements.
However, such electro-mechanical systems suffer the disadvantages of excessive space requirements, excessive weight, and excessive costs. Moreover, in certain applications--such as in aircraft systems--the necessity of performing very complex functions has necessitated the design of very complex circuitry, with attendant disadvantages related to cost, size, weight, heat dissipation, and inherent unreliability.
In order to overcome the above disadvantages, electromechanical relays and thermal overload devices have been replaced by solid state power controllers which, for example, employ silicon-controlled rectifiers (SCR) to perform power switching and circuit breaking functions. Such solid state power controllers are disclosed in U.S. Pat. Nos. 3,504,204 and 3,879,652. Such power controllers have typically contained zero crossover circuits associated with control logic in order to control the solid state switch in accordance with the zero crossings of an AC source waveform applied to the load. Furthermore, such systems have also typically included complementary SCR devices for controlling respective half-cycles of an AC source voltage.
Such zero-crossing SCR control systems have been adapted for flexibility so as to be usable for both single-phase, full-wave and three-phase operations. Such a system is disclosed in U.S. Pat. No. 3,577,177, as well as in IBM Technical Disclosure Bulletins authored by L. A. Smith (Volume 11, No. 5, October 1968, page 501) and by L. M. Ernst and T. L. Wells (Volume 15, No. 3, August 1972, page 734), and in RCA Application note ICAN-6268 dated June 1970, authored by H. M. Kleinman and A. Sheng.
Power control systems have been designed for various modes of "trip" initiation. That is, actuation of the power controller so as to block the application of power to a load may be multi-mode in that different modes of "trip" operation are actuated in response to various respective conditions in the circuit such as catastrophic overcurrent (necessitating immediate "trip") or moderate overcurrent (necessitating less immediate action ("timed trip")). Such a multi-mode "trip" operation is disclosed in U.S. Pat. No. 4,038,695.
Such prior art multi-mode "trip" operation has been, however, burdened by several disadvantages. Firstly, such systems have not taken advantage of advanced solid state circuitry to include digital mechanization of trip timing and control functions (as, for example, by mechanization via a monolithic integrated circuit (IC) device). Secondly, such systems have not been sufficiently sophisticated or precise in their operation, and thus have not been capable of simultaneously considering, and incorporating into trip time computations, both the transient current value and the time duration of the overcurrent. Thirdly, such systems have not been flexible so as to provide a power controller which is pre-settable for switch operation in either the "normally open" (NO) or "normally closed" (NC) modes of operation. Fourthly, such systems have not had the capability of validating control signals, applied to the system such as "turn on" and "turn off" control signals. Finally, such systems have not been capable of achieving stability in various environments, and thus have not been immunized from noise, temperature, vibration, and a nuclear environment. Such immunity is, of course, particularly necessary when such power controllers are employed in modern aircraft control systems.